Charging batteries with my TIG welder

trazor

100 W
Joined
Jan 13, 2015
Messages
171
I don't know if this is a new idea, but maybe it is worth posting it here.

[youtube]7Eh-Oe7oqIo[/youtube]

For my new emoto (https://endless-sphere.com/forums/viewtopic.php?f=28&t=92563&p=1377533&hilit=openemoto#p1423299) I was in need of a charger capable of 18s. I didn't have one and it is expensive to buy one and bring it here (I live in Uruguay). More power=more weight=more shipping costs. So I imported a light DC boost converter and plugged it to my welder (in stick mode).
I can get 1200W from this setup, so I think I will purchase another DC boost converter to charge my 20s batteries because this looks really powerfull and cheap. In some countries it is probably cheaper to purchase a DC welder (under usd 80) and import a lightweight DC boost module (34 usd) to charge >~ 45v batteries using this method.

There are some caveats though. Welders don't output constant voltage, so when the load decreases, maybe voltage goes higer. If this voltage is higher than the end voltage of your battery, it can overcharge. Every welder has different floating and loaded voltages. Be careful.

This experience made me think about some other issues:
This type of charging (with any CC-CV source) will not do cut off at the end voltage. Batteryuniversity.com says:

Li-ion cannot absorb overcharge. When fully charged, the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To minimize stress, keep the lithium-ion battery at the peak cut-off as short as possible.
https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

I see here a lot of people charge with CC-CV sources... the finish stage of cut-off can be ignored?, by how far? it is OK if I disconnect the source 1 hour after end current is reached? 12hs? 24hs?

To overcome the missing cut off in the power source, I had this idea, maybe is not practical or safe.... configure the CC-CV source to go about 2 volts higher than the battery full voltage, and let the BMS do the cut off. BUT, this changes the gradual ramp off, making a very "brute" charge. I read somewhere that lithium batteries must be charged slowly after 80%. Because? Safety? Battery longevity?

This makes me think another question... in proper chargers.. this current ramp down is made artificially (by a microcontroller) or it is plain Ohms law?

I want to hear your opinions. Thanks!
 
If the info is any help, there have been a couple of other discussions about using welders as/with chargers:

https://endless-sphere.com/forums/search.php?keywords=Charg*+welder&terms=all&author=+&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search
 
amberwolf said:
If the info is any help, there have been a couple of other discussions about using welders as/with chargers:

https://endless-sphere.com/forums/search.php?keywords=Charg*+welder&terms=all&author=+&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

Thanks Amberwolf. The threads are interesting and I learnt about the bad power factor and crappy duty cycles (even if welder claim 60% at minimum). Sadly, my other questions remains unanswered :(
 
I brought the cheapest welder to charge my two e-motos in 1 hour (18s and 20s, about 800W/h per battery). I'm melting my garage wall sockets :( I need to lay a better power line to my garage now
I'm taking about 2.5KW of power from the welder, the measurements at the socket (with a tp-link smart plug) are 2.88KW, so efficiency is not great. Anyway I consider this a good solution if you only have welders at your disposal :) The welder voltage sags from 65 to 32 when full power is demanded. Currently the limit is imposed by the DC-DC boost converters. I don't reach the declared 60% duty cycle time of the welder.

Here are some images:

View attachment 1
IMG_20181202_042836.jpg
 
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